Did you look at Cinelerra, linked fron the Avidemux page (under the head "Open source software similar to Avidemux")?

"Cinelerra is a highly advanced and professional video editing, but still remains open source. Cinelerra solves three main tasks: capturing, editing and compositing."

It may not satisfy all your requirements (depending, in part, on your background in AV editing), but seems to be worth a look.